'97 5.7 Thermostat

My thermostat is stuck open, I think. The temp is running about 150 to 160 and my mileage dropped. The thermostat bolts are both REALLY tight. Any hints on how to loosen them without damaging anything in the process???

For fasteners like the tstat bolts, I like to shock them without over torquing them. One of my favorite tools for this is the impact driver. The vibration and the incremental torque tends to get most screws, nuts, and bolts loose. If you have to replace the bolts, avoid dissimilar metals, and chase the threads in the block.